Subaru O2 Sensor Failure Draining Gas Tank Fast

As someone with some experience working on similar issues, I dealt with nearly identical symptoms on a Subaru Stella 2016 last year. The check engine light and poor fuel economy definitely match what you're describing. After sensor testing, it turned out the problem wasnt the oxygen sensor itself, but rather a damaged connection in the wiring harness. The workshop found the plug connection was corroded and making poor contact with the sensor. The repair took about 2 hours and cost 95€, which included diagnostic time and fixing the faulty sensor connection. After the repair, fuel consumption returned to normal and the malfunction indicator disappeared completely. To provide more specific advice about your situation, could you share: current mileage on your vehicle? When was the last time the oxygen sensor was replaced? Are you noticing any rough idling or hesitation during acceleration? Have you had any recent work done near the exhaust system? These details would help determine if your issue matches what I experienced or if you might be dealing with something different.

Thanks for sharing your experience. My Pleo has 197641 KM and the last service was done 3 months ago, where they checked the exhaust system but didnt mention any sensor issues. Now Im experiencing rough idling, especially when cold, and the malfunction indicator comes on intermittently. Based on your experience with the wiring harness, I will have the connections checked before replacing the entire heater element. The fuel consumption increase matches what you described, so Im hopeful its a similar wiring issue rather than a complete sensor failure. Have you noticed any warning signs return since your repair was completed?

Thanks for those details about your Pleo. On my Stella, the symptoms started very similarly with the rough cold idle and intermittent check engine light. Since the repair of the wiring harness, I havent experienced any return of symptoms or issues with the air-fuel ratio. The mileage on your vehicle suggests its worth checking both the wiring and the heater element. My repair has held up perfectly for over a year now, but I learned during the diagnosis that oxygen sensor issues often show a pattern, they typically start with intermittent problems that become more frequent over time. The fact that your recent service included an exhaust system check but didnt flag any sensor issues actually mirrors my situation. The corroded connection wasnt visible during a standard inspection. It required specific sensor testing to identify the fault in the wiring. For your peace of mind, get the workshop to perform a complete diagnostic of the heater circuit. In my case, what initially looked like a sensor failure was resolved without needing a full replacement. The repair has proven reliable, with fuel consumption staying consistently normal since the fix.

My vehicle has exactly the same symptoms, and your experience with the wiring harness seems really relevant. My mechanic is scheduled to look at it tomorrow, and Ill definitely have them check the connections before jumping straight to replacing car components. The malfunction indicator behavior you described matches mine perfectly, especially that pattern of intermittent problems becoming more frequent. Its reassuring to hear your repair has held up well for over a year without any recurring vehicle emissions issues. The rough cold idle is particularly concerning, but knowing it could be related to a simple wiring issue rather than a complete faulty sensor failure gives me hope for a cost-effective fix. I appreciate you sharing the specific details about the diagnostic process that found your corroded connection. Ill update once I get the results from my workshop. Hoping its just a wiring harness issue like yours and not a complete sensor replacement. The 95€ repair cost you mentioned would be much better than the several hundred I was quoted for a new oxygen sensor.